In Bluetooth®, a network includes a master which performs polling control for communication timing control and access control of a communication device, and a slave which performs communication in accordance with a signal from the master. One master and at most seven slaves can construct a piconet. In order to connect the communication device belonging to the Bluetooth® network to a LAN, an access point serves as the master, and the communication device connected to the network serves as the slave. In Bluetooth®, a frequency hopping spread spectrum scheme is used. In the piconet, communication time division multiplex (time division slot multiplex) is performed for each slot, and a plurality of terminals in the piconet can communicate with each other. Since a slot synchronous state must be maintained, all the terminals in the piconet have counters called Bluetooth clocks. In one piconet, in order to match the Bluetooth clock value of the slave with that of the master, a clock offset which is a shift between the Bluetooth clock values of the slave and master is calculated. Accordingly, the clock synchronous state can be maintained by adding (subtracting) the offset value to (from) the Bluetooth clock value of the slave. The terminals in a single piconet have the same frequency hopping pattern. Hence, the terminals can communicate with each other.
Bluetooth® defines the following arrangement (to be referred to as a scatternet hereinafter). When the communication device currently connected to the access point (a piconet) is to participate in another piconet (e.g., a new piconet including a communication device such as a PC), the communication device shifts to a power saving mode in which intermittent reception is temporarily performed in communication with the master (in this case, the access point) which controls the current piconet. Then, the connection with the access point is released, and communication is performed after switching to the communication timing of the new piconet (e.g., see non-patent reference 1).
[Non-Patent Reference 1]
“Technology KAITAISINSHO Bluetooth™ Technical Interpretation Guide” edited by Japan Ericsson, written by Kazuhiro Miyazu, Ric Telecom, pp. 39-41, pp. 181-185).
In a Bluetooth® piconet operation, the communication devices (slaves) communicate with each other via the master which controls an access timing. Accordingly, a traffic increases in a radio section, and data cannot be efficiently transferred. In the scatternet operation described as a means for avoiding this problem in the prior art, access timing control for a specific slave device (to be referred to as a slave 1 hereinafter) is performed by determining the access timing in accordance with the power-saving mode timing set between the slave 1 and master which operate asynchronously. Hence, the initially set access time cannot be ensured in accordance with clock frequency shift between the masters.
When the communication traffic between the slave 1 and the master, and the communication time between the slave 1 and another master are to be changed, a power saving mode shift time between the master and the slave 1 must be reset. Hence, it is difficult to sequentially accommodate the access time in accordance with a change in traffic. As a means for solving this problem, a method of notifying of a period (communication hold period) in which the slave capable of participating in the plurality of piconets does not participate in the piconet has been studied. However, a method of notifying the master of the communication hold period has not been disclosed yet, and it is difficult to perform access control in accordance with a communication condition such as the traffic.
As described above, in a radio communication scheme in which one radio communication terminal can belong to the plurality of radio networks at the same time, a timing for accessing/inaccessing to each of the networks must be arbitrated. However, this arbitration is difficult.